1. Field of the Invention
This invention has to do with electronic circuitry which can be used, for example, in computer graphics processing. In particular, this is a compact logic circuit which can perform a selection of functions and be integrated on the same substrate as random access memory (RAM) device.
2. Description of the Related Art
An introduction to the device is now presented, with reference to FIG. 1. A multifunction logic circuit L is included, for example, as part of a RAM. It performs a logic function on logic signals D and M, D and M having either a high or low logic level, and stores the output in STORE, which typically might be a RAM cell under access. In this case the logic function is determined by specific design criteria. Multifunction logic circuit L takes as inputs an existing stored bit M, an input data bit D (taken through a RAM input port, not shown), and control signals C.
Typical logic functions include CLEAR, the output low, and SET, the output high, as well as various combinations of AND, OR, and XOR on inputs M, D, and inversions thereof. A logic function in effect until another selection is made. remains in effect until another selection is made. The logic operation is performed whenever data is written through the RAM input port.
This device has great utility in computer graphics applications, where a graphic field mapped in RAM is altered by rastering new values into selected RAM locations.